72 NATURE AND LIFE. 



teristic of the anatomical elements is evolution, quite dis- 

 tinct from nutrition. These little bodies, at the instant 

 when they make their appearance, are not like what they 

 are about to be at a later time. The more remotely from 

 the moment of their birth we consider them, the more dif- 

 ferent is the aspect we observe them to present from that 

 they formerly had. They gain a larger bulk, and compli- 

 cate themselves with new parts, with more perfect forms, 

 which will vanish in their turn, so that every element thus 

 describes a curve of evolution, of which the apex, repre- 

 senting the full-grown state, is reached more or less rapidly. 



If nutrition and evolution belong to all anatomical ele- 

 ments, contractility is the privileged mark of a very small 

 number among them. It is peculiar to muscular fibres, in 

 which it presents two modes : In the striated muscular 

 fibres of animal life, it is sudden and quick ; in the smooth 

 fibres of organic life, it takes place slowly. It is upon this 

 property that all movement and locomotion depend, since it 

 is that which gives force to the muscles. * 



Innervation is the peculiarity of the nerve-elements. 

 Its manifestations are complex and diversified, but it is 

 specially marked above all by this fact, that, far from lim- 

 iting its play to a local action, it radiates from a distance 

 and carries its influence far along. The nerve-cell, in fact, 

 finds in the nerve-tubes issuing from it, in the congenerate 

 cell which is appended to it, either conducting apparatus, 

 designed to carry off the force which it produces, or a true 

 receiving apparatus, designed to store up that force, and 

 propel it at a distance under another form. A real electro- 

 dynamic pair, as M. Luys has so well expressed it, the 

 nerve arrangement thus reduced to its simplest expression, 

 itself engenders the force which it transmits afar. It con- 

 ducts, receives, and transforms it in the manner of those 

 machines for electric transmission which represent, in the 

 apparatus for generating electricity, the emitting cell in 



